1. Field
Embodiments relate to a light-emitting device.
2. Description of the Related Art
Light-emitting devices are devices that convert electric energy into light energy and are capable of realizing various colors by adjusting the composition ratio of compound semiconductors.
When a forward voltage is applied, electrons from an n layer and holes from a p layer are combined to emit energy corresponding to an energy gap between a conduction band and a valence band. The energy is generally emitted in the form of heat or light. In light-emitting devices, in particular, the energy is emitted in the form of light.
Nitride semiconductors, for example, are attracting much attention for the fields of optical devices and high power electronic devices because of their high thermal stability and wide band gap energy. In particular, blue light-emitting devices, green light-emitting devices, and ultraviolet (UV) light-emitting devices that use nitride semiconductors have been commercialized and are widely used.
In related-art lateral light-emitting diodes (LEDs), a GaN epitaxial layer is grown on a patterned sapphire substrate, and p- and n-electrodes are formed with the use of a mesa structure.
The distribution of light in a related-art lateral LED shows that about 30% of light is emitted from the top of a GaN epitaxial layer and about 70% of the light is emitted from the bottom of a patterned sapphire substrate. More specifically, in a related-art lateral LED, most light is emitted from the bottom of the patterned sapphire substrate at a predetermined angle. That is, due to the total reflection caused by the difference between the refractive index of the patterned sapphire substrate and the refractive index of the air, most of the light beyond a predetermined critical angle cannot be emitted regardless of the presence of the patterned sapphire substrate.